F. Zocca, F. Roncarolo, B. Cheymol, A. Ravni, H0/H- current monitor F. Zocca, F. Roncarolo, B. Cheymol, A. Ravni, S. Burger, G.J. Focker, J. Tan BE/BI Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

Outline H0/H- current monitor overview: Concept & specifications Geometry & beam dynamics Material Sensitivity & expected signals Status & on-going developments Importance of the “half-chicane section” test for instrumentation Other advantages in case of test implementation in L4T line (after bending) F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

H0/H- current monitor concept B.Goddard et al., 2010 H0/ H- current monitor needed in front of the dump - to allow efficient setting up of the injection - to monitor the efficiency of the stripping foil (detect degradation and failure) The H0/H- current monitors are supposed to be plates intercepting the H0 and H- ions and acting as a Faraday cup for the stripped electrons (stripping & collection) F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

Functional specifications Robust and simple (lifetime ≈ 20 years, no maintenance) Radiation dose of 0.1-1.0 MGy per year Vacuum level 10-8 mbar with beam Withstand the BSW4 pulsed magnetic field of 0.4T and at the same time do not perturb the field by more than ≈ 1 % Transverse dimensions (including support structure) not exceeding dump dimensions Sensitive areas maximized to cover as much as beam halo as possible Withstand the heat load in normal operation condition and a full Linac4 pulse load (2.5×1013 H- ions), in case of failure of the stripping foil, on a one-off basis, several times per year Dynamic range: 5×107 – 5×1012 ions (for H- and H0 alike) Absolute accuracy ± 20 %, relative accuracy ± 10 % Time resolution: integral over the full injection time (few ms – 100 ms) – however higher resolution is welcome F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

Monitor geometry preliminary proposal Top view Missing on the front frame only Signal plates Polarization frames F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

SiC Dump 110 mm + 30 mm Pol. Frames Beam envelopes SiC Dump 110 mm + 30 mm Pol. Frames Courtesy of C.Bracco Separation H0/H- = 10.8 mm Separation H0/H+ = 2.8 mm Distance dump edge/ H0 beam = 0.5 mm F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

Plates material: titanium Requirements: good enough conductivity (for signal read-out) but compatible with BSW4 field quality, low thermal load, low neutron yield (low activation), high signal level Fully acceptable Among low-Z conductive materials, titanium is the only one with acceptable impact on the BS4 field quality thanks to the relatively “low” conductivity Acceptable (not ideal) Not acceptable Material Conductivity (1/Wm) (for signal read-out) Thermal load (DT) for a full Linac4 pulse Melting point Neutron yield (w.r.t. n° of protons) Signal Q (e/H-) with NO external fields* Q (e/H0) with NO external fields* Compatibility with BS4 field Graphite 6.1 × 10 4 67 K 3773 K 0.41 % - 1.83 - 0.90 YES Aluminum 3.77 × 10 7 50 K 933 K 0.57 % - 1.63 - 0.80 NO Titanium 2.34 × 10 6 80 K 1933 K 0.99 % - 1.42 - 0.70 Copper 5.96 × 10 7 98 K 1356 K 1.0 % - 1.22 - 0.60 Tungsten 1.89 × 10 7 229 K 3683 K 6.4 % - 0.68 - 0.33 * taking into account losses due to electron backscattering and secondary emission F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

Charge signal estimate Proton energy = 160 MeV  electron energy = 87 keV Q (e/H-) = -2*(1-h) + 2*SEYP + 2*SEYBS + YD h = fraction of backscattered electrons (e- energy range ≈ 1-87 keV) SEYP = Secondary Emission Yield of the Proton (e- energy range ≈ 1-20eV) (SEY of H- entering the plate = SEY of proton exiting) SEYBS = Secondary Emission Yield of one BackScattered electron YD = fraction of “delta-rays” electrons emitted by the plate owing to collisions with the proton beam (e- energy range ≈ 100-400 keV) Q (e/H0) = - (1-h) + SEYP + SEYBS + YD Material h SEYP SEYBS YD Q (e/H-) Q (e/H0) Titanium 0.23 0.038 0.0114 0.025 - 1.42 - 0.70 F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

Polarization rings: E-field effect View from the top CST Particle Studio tracking simulation Electron energy range = 10-30 eV Isotropic angular distribution Stationary condition No space charge frame (- 1000 V) monitor plates frame (- 1000 V) E-field map on the monitor plates Effect due to the missing lateral frame Simulations including surrounding beam pipe F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

E-field + B-field effect (BSW4 magnet 0.4T) Uniform vertical B-field of 0.4 T Stationary condition, no space charge 10 mm Secondary emission electrons (10 eV - 30eV) Curvature radius for 30eV electrons ≈ 30 mm Backscattered electrons (60 keV – 90 keV) Curvature radius for 90keV electrons ≈ 2.6 mm “Delta-rays” electrons (125 keV – 375 keV) Curvature radius for 375 keV electrons ≈ 6 mm F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

Expected signals Stripping foil of ≈ 200 mg/cm2 : H- stripped to H0 ≈ 1 % , H- stripped to H+ ≈ 10-6 level BUT assume that 1% of H- from the LINAC4 beam will miss the foil and impact the dump  nominal number of particles hitting the monitor per injection = 2.5 × 1011 for H0 and H- alike Desired dynamic range = 5 × 107 - 5 × 1012 particles (for H- and H0 alike) Q (e/H-) Average Pulse Current MIN Average Pulse Current NOM Average Pulse Current MAX H- SEY + BS + YD  - 1.42 113 nA 0.56 mA 11 mA BS + YD  - 1.52 121 nA 0.6 mA 12 mA Full deposition  -2 160 nA 0.8 mA 16 mA H0 SEY + BS + YD  - 0.70 56 nA 0.28 mA 5.6 mA BS + YD - 0.75 60 nA 0.3 mA 6 mA Full deposition  -1 80 nA 0.4 mA 8 mA F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

Status Almost finalized: Material choice Design principle Theoretical study of sensitivity – range of expected signals On-going developments: Final dimensions (w.r.t. dump size & beam dynamics simulations) Mechanical support Final integration in the system (design office) Simulation of the impact on the BSW4 field (by magnet group) Cables type and quantity Read-out electronics F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

What is important to test Operational check including mechanical integration issues, thermic and mechanical stress (beam heat load and magnetic field) Impact on the BSW4 field quality – beam positions & envelopes Sensitivity to H- and H0 ions: effect of the E-field and of the B-field on the secondary electron suppression (and eventually on the backscattering effect suppression) Read-out electronics: noise level and amplitude of picked-up induced signals on the plates  decision between charge integration or current read-out mode Control signals for start/stop read-out according to injection start/stop Calibration procedure of the H- and H0 currents: with unstripped H- beam of known intensity, profiting from BLMs for H0…? Interlock reaction (protecting the injection system) Long-term stability of the measured signals F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

The presence of the bending magnet L4T.MBH.0250… … allows us for a more complete test of the laser-wire scanner Test of the stripping unit (≈ 20 cm) 40 cm long slot allocated between the steerers L4T.MCHV.0115 and L4T.MCHV.0135 for installing a laser station + profile monitor via stripped electron counting F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013

Conclusions “Half-chicane section” test is of extreme importance for instrumentation commissioning Despite the relatively simple working principle, many issues need to be checked for the H0/H- current monitor, regarding - mechanical integration - measurement sensitivity & read-out electronics - interlock system Beam instrumentation developments (laser wire emittance meter) would much profit from the presence of the bending section  we strongly support the option of the “half-chicane section” test in the L4T line F.Zocca - Linac4 BCC Meeting 43 - H- stripping test - 23rd April 2013